In the information-oriented society in recent years, the amount of data to be stored in a recording medium is continually increasing. For this reason, a recording apparatus and a recording medium with an outstandingly high recording capacity have been desired. Also, hard disks, which are currently in an increasing demand as an economical recording medium of high capacity, are expected to be required to have recording density of 1 tera-bit or more per square inch, which is ten times the current density, in coming years.
In a magnetic recording medium used in conventional hard disks, a predetermined region of a thin film including polycrystals of magnetic fine particles is used as one bit for recording. In order to increase recording capacity of a magnetic recording medium, the recording density should be increased. In other words, it is necessary to reduce the recording mark size which is usable for recording of one bit. However, when the recording mark size is simply reduced, the influence of noise which depends on the shapes of magnetic fine particles becomes nonnegligible. If the particle size of magnetic fine particles is reduced to lower the noise, a problem of thermal fluctuation occurs, which makes it impossible to maintain recorded data at a room temperature.
In order to avoid these problems, a bit patterned medium (BPM) has been proposed, in which the recording material is separated by a nonmagnetic material in advance, and a single magnetic dot is used as a single recording cell to perform read and write.
In magnetic recording media installed in HDDs, there is an arising problem of the interference between adjacent tracks which inhibits improvement in track density. Particularly, reducing a fringe effect of a write head field is a significant technical problem to be solved. To solve this problem, there has been developed a discrete track recording-type patterned medium (DTM), in which the magnetic recording layer is processed so that the recording tracks are physically separated from each other. In the DTM, it is possible to reduce side erase which erases information in the adjacent tracks in writing and side read which reads information in the adjacent tracks in reading. On this account, the DTM is promising as a magnetic recording medium capable of providing a high recording density. Incidentally, it should be noted that the term “patterned medium” as used herein in a broad sense includes the bit patterned medium and DTM.
With respect to methods for manufacturing the BPM and the DTM as described above, there are known a method wherein a pattern of protrusions and recesses is formed on the surface of a magnetic recording layer by way of fine working such as etching, and a method wherein a pattern consisting of magnetic regions and non-magnetic regions of a magnetic layer is formed by way of chemical treatment. With respect to the latter method, various methods are known, including, for example, a method wherein specific regions of the magnetic recording layer are exposed to a magnetically deactivating gas to thereby deactivate the magnetism of the specific regions, a method wherein specific regions are deactivated by the injection of an ionized element by making use of a plasma beam, etc., and a method wherein a deactivating material is deposited on specific regions to thereby allow the material to diffuse into the specific regions.
In spite of these conventional techniques now available, it is still demanded to manufacture a magnetic recording medium wherein the magnetism of non-recording regions of the magnetic recording medium can be efficiently and sufficiently deactivated.